The present invention relates generally to systems for monitoring electrical power circuits and particularly to a programmable system for measuring and calculating electrical parameters from multiple power circuits.
The monitoring of electrical power is important to ensure that this energy resource is effectively generated, distributed and utilized. Utilities need to measure power coming out of a generation station or going into a power station. In addition, to minimize power transmission losses, it is important to minimize the phase relationship between the current and voltage waveforms of the power being transmitted. In industrial control applications, it is important to be able to continuously monitor the current and phase of the power into a machine which may vary with the machine load.
Traditional systems for monitoring power circuits require the installation of individual measuring devices to measure a specific power system parameter; for example, Watts, Vars, Amps, or Volts. These devices typically comprise discrete analog transducers which convert AC voltage and current signals from a power system into DC output signals proportional to the true power on the system. For example, typical utility revenue kilowatt hour meters measure power in an analog fashion. Where a data acquisition system must measure numerous circuits, requiring separate measuring devices for each circuit can add greatly to the overall cost of the system. Also, where a number of circuits are being remotely monitored for computer processing and display, the individual devices must be connected to a data acquisition device and suitably processed to interface with the computer. Further, multiple measuring devices greatly increase the overall error of the system.
Accordingly, it is a principle objective of the present invention to provide a simplified system for measuring various parameters in multiple power circuits to reduce the cost of purchasing, installing and maintaining the system.
More specifically, it is an objective of the present invention to provide a system in which a single measuring device measures the fundamental parameters in a power system so that subsequent derived parameters can be computed in a controller data processing computer, thereby eliminating the necessity of multiple measuring devices.
It is another objective of the present invention to provide a power analyzer which reduces the cost of maintenance of the overall system.
It is an additional objective of the present invention to provide a power analyzer which has very high precision through self calibration and a non-synchronous measurement technique.
It is still another objective of the present invention to provide a microprocessor controlled power analyzer that can continuously and rapidly monitor a plurality of circuits.
To achieve these foregoing objectives, the present invention provides a high speed power analyzer which utilizes voltage and current input devices, such as transformers, for transmitting signals proportional to the voltage and current levels in the circuits being measured. The signals are transmitted to a multiplexer and the output of the multiplexer is coupled to an analog to digital (A to D) converter for converting the voltage and current signals into a digital representation of same. A digital processor circuit is coupled to the multiplexer for selecting which inputs are coupled to the multiplexer outputs. The processor circuit also is coupled to the A to D converter to receive the digital voltage and current signals. The processor circuit continuously samples and stores the voltage and current signals at regular intervals of time and also calculates and stores a plurality of electrical variables related to the power used by the circuits. For example, these electrical variables may include frequency, RMS volts, RMS amps, and the phase angular relationship between the voltage and the currents in the system.
In one form of the present invention, the system includes a host computer coupled to the digital processor circuit for performing additional calculations on the electrical variables to thereby derive electrical parameters relating to the performance of the power circuits. These parameters may include Watts, Watt-hours, Vars, Power Factor, etc.
Another feature of the present invention, is that the software of the processor circuit performs continuous functions such as calibration, drift and offset compensation and zero cross detection. In addition, the system samples the input devices rapidly and continuously in a manner which is not synchronized to the power waveforms being sampled. Specifically, in one form of the present invention, the system samples five channels at a rate of 1199 times each second.
Additional advantages and features of the present invention will become apparent from a reading of the detailed description of the preferred embodiment which makes reference to the following set of drawings.